ANTEOPHYTA. 237 



441. The fibro- vascular bundles are of the collateral 

 form, the only exception being the first-formed bundle in 

 the root, which is of the radial type. The bundles are 

 symmetrically arranged in the stem, through which they 

 run nearly parallel to each other, and extend into the 

 leaves ; a few, however, have no connection with the 

 leaves. 



442. All the kinds of tissues, with the exception of thick- 

 angled tissue, may occur in the bundles ; but they are 

 mainly made up of tracheary, sieve, and fibrous tissues. In 

 the larger perennials, as the trees, the great mass of tissue 

 in the woody stems is principally made up of the tracheary 

 and fibrous tissues of the fibro-vascular bundles. In suc- 

 culent organs and the stems and leaves of water-plants, 

 the bundles are usually smaller and more simple, being 

 sometimes reduced to a thread of tracheary or sieve tissue. 



443. Of the remaining tissues soft tissue, in its various 

 forms, is by far the most common. The hypodermal por- 

 tions are frequently composed of thick-angled or stony 

 tissue. Milk-tissue is common in certain families. 



444. The organs of reproduction in all flowering plants 

 are modifications of the type found in the higher Fern- 

 worts. The leafy plant produces two kinds of cells, an- 

 swering to the microspores and macrospores we have lately 

 studied. Moreover, these cells are produced, as in Fern- 

 worts, upon more or less modified leaves. 



445. The microspores, commonly called pollen-cells, de- 

 velop in great numbers within sac-like enlargements (micro- 

 sporangia or anthers) upon certain modified leaves (micro- 

 sporophylls or stamens). They are set free by the breaking 

 of the sac, and are borne away by the winds, by insects, or 

 other means. 



